Tissue - Epithelial Flashcards
Major differences between Epithelial tissue and connective tissue
- Number of cells in tissue - epithelial has more cells tightly packed in the extracellular matrix
- Epithelial has no blood vessels - exceptions connective tissue having a large network (except cartilage) and epithelial lining
How do epithelial tissue and connective tissue relate to each other?
Epithelial tissue being avascular is often next to connective tissue which has a network of blood vessels. Thus, epithelial tissue and connective tissue can exchange substances when Exhange with blood is necessary = oxygen, nutrients and waste.
Arrangement of epithelial tissue
Single of multiple layers of sheets. Forms covering and lining in body. Not covered by another layer - has a free surface. Apical (free_ surface and basal surface bottom - polar.
Major purpose of epithelial tissue
Protect , absorb, filtrate and secrete. Selective barrier.
How are epithelial tissue classified ?
- Based on arrangement of cells in layer.
- Cell shape
Types of arrangement of cells in + desciption in regards to epithelium cells
- Simple epithelium - single layer, diffusion, filtration, secretion and absorption.
- Pseudostratified epithelium - single layer, nucleus different levels and cells don’t always reach apical surface. Can have cilia or goblet cells that secrete mucous.
- Stratified epithelium - more than two layers, protect underlying tissue in locations where wear and tear.
Types of cell shape + description
- Squamous - flat and thin, allow for rapid passage through them
- Cuboidal - tall as they are wide like cubes or hexagons. Can have microvilli on apical surface which secretes and absorbs.
- Columnar - taller than wide. Protect underlying tissue. Apical surface can have cilia or microvilli, often specialized in secretion and absorption.
- Transitional - change shape
Simple squamous
- Single flat layer
- Centrally located nucleus
- Oval or spherical in shape
- Filtration (blood in kidneys) and diffusion (oxygen into blood vessels) and secretion (at serous membranes)
- Not found at a site that undergoes mechanical stress
- Found in cardiovascular and lymphatic system
Simple cuboidial
- Sinele layer, cube shaped cells
- Nucleus centrally located
- Secretion and absorption
- Some glands such as thyroid and lines capsule of the eye
Simple columnar
- single layer of column
- oval nucleus near base
- can have microvilli (increasing rate of absorption)
- Can have goblet cells, which secrete mucous
- Lines gastrointestinal tract, duct of many glands.
Pseudostratified columnar
- appear several layer because nuclei are various levels
- all cells attached to basal membrane
- some cells do not extend to apical surface
- Can have goblet cells or cilia
- Secrete mucous (if ciliated), and sweep mucous away
- No cilia- absorption and protection
- Line upper respiratory tract, line duct of many glands, part of male urethra.
Stratified squamous
- 2 or more layers
- Cells deeper may be more cuboidal and columnar
- as basal cells divide, cells push up to apical layer
- as they move to the top, blood supply decreases, become more dehydrated and less metabolically active.
- tough proteins start to dominate, cells become tough
- at apical surface, cells are dead
- Keratinized - at apical layer mainly - protects skin and underlying tissue from heat, microbes and chemicals
- Non-keratinized - moistened by mucous from salivary and mucous glands
- Keratinized - superficial layer of skin
- Non keratinized esophagus, and covers tongue
- protects (abrasion, heat, UV ) and defense against microbes
What type of epithelia tissue can could be keratinized or not ?
Stratified squamous
Stratified cuboidal
- two or more layer
- cells in apical layer more cube shape
- protection, limited secretion and absorption
- rare
- ducts of adult sweat gland and esophageal glands
Stratified columnar
- Basal layer usually shorter and irregular shaped cells
- Only apical layer columnar
- rare
- protection and secretion
- Line esophageal glands, urethra
Transitional
- variable appearance
- relaxed - stratified cuboidal except top layer which tends to be large and rounded
- stretched - flatter and stratified squamous
- multiple layer and elasticity makes it ideal for lining hollow structures
- Allows urinary organs to stretch and maintain protective lining while holding variable amounts of fluid
- Lines urinary bladder and portions of ureters and urethra
What is a gland ?
Single cell or group which secretes a substance into ducts or the surface or into blood.
What are the categories of gland ?
Endocrine or exocrine
Endocrine gland, describe and give example
- Secretes hormones
- Hormones go to interstitial fluid before entering the bloodstream
- Does not enter a duct
- Far reaching effects as can be distributed throughout the body via the bloodstream
- Thyroid, pancreas and ovary
Exocrine gland
- Secretes products into ducts
- Ducts then empty onto the surface of a covering and lining epithelium
- Secretion can have limited effects and can even be harmful
- Pancreas
- Substances include oil, earwax, saliva and digestive enzymes
Can glands be a mix of endocrine and exocrine ? Give example
Yes, pancreas, testes and ovary